1. Field of the Invention
This invention relates to a die for the attachment of a label to the surface of an article. More particularly, this invention relates to a die for heating a label provided on one surface thereof with an adhesive layer and attaching the heated label uniformly and tightly to the surface of a flexible article.
2. Description of the Prior Art
The flexible containers such as blood bags and transfusion bags by nature require attachment to their surface of a label displaying the kind, attributes, etc. of their contents. To date, the practice of preparing a pressure-sensitive label provided with an adhesive layer capable of exhibiting viscosity at normal room temperature and attaching this pressure-sensitive label fast to such flexible articles as the flexible containers mentioned above has prevailed. The pressure-sensitive label so attached to the surface has tended to peel off spontaneously or to be readily peeled off intentionally because the adhesive force of the pressure-sensitive label of this nature is generally weak and the viscous force of the adhesive layer is deteriorated by aging. When the label indicating the blood type (the ABO system, the pH system, etc.) and attached to the blood bag, for example, happens to be peeled off or intentionally or accidentally replaced by other label, there arises the possibility that incompatibility of blood type will occur at the time of transfusion and a serious accident such as fatality on the part of a patient subjected to transfusion will ensue. The use of the pressure-sensitive label of this nature, therefore, can not be called very adequate.
Recently, from this point of view, the method which comprises preparing a label provided on one surface thereof with an adhesive layer formed by the application of a thermosensitive adhesive agent, heating the label, and applying the heated label to the surface of a flexible article has been finding popular acceptance. Since the adhesive force due to the thermosensitive adhesive agent is strong at normal temperature and is deteriorated only slightly by aging, the problem of the peeling of an attached label mentioned above does not occur so long as the label is thoroughly heated and attached uniformly to the surface of the flexible article.
Heretofore, for the purpose of effecting continuous application of such labels to a plurality of flexible articles, it has been customary to prepare a die provided with a suction hole communicating with suction means, keep a suction surface of the die heated as with a heater, cause labels to adhere tightly one after another to the heated suction surface and allow the thermosensitive adhesive agent on the labels to melt, and apply the label by pressure tightly to the surface of flexible articles intended for application of label. Since the suction surface of the die is flat and smooth, when the label which is thin and pliable is attached by suction tightly to the suction surface, there ensues the possibility that a small amount of air is entrapped in the form of clusters of air between the suction surface and the label. In the portion of the label under which such clusters of air are formed as described above, the adhesion of the label to the suction surface is inferior because the clusters of air function as an insulating layer and consequently prevent the heat of the die from being amply transferred to the thermosensitive adhesive agent. Moreover, since the surface of the flexible article such as the blood bag which is intended for application of the label is liable to form a jogging contour particularly when the article is filled with its content, the ambient air finds its way between the label and the surface of the flexible article at the time that the label attached tightly to the die is pressed against the flexible article. In the portion of the label under which the air is entrapped, the label is prevented from contacting the surface of the flexible surface and consequently kept unattached thereto. When the portion of such inferior attachment or no attachment occurs near the edge of the label, even the label using a thermosensitive adhesive agent has the possibility of peeling off the flexible article.
An object of this invention, therefore, is to provide a die for the attachment of a label to a flexible article, which die is improved so as to eliminate the problems heretofore encountered in the attachment of a label to a surface as described above. This invention further concerns a label-attaching die which is adapted to heat a label provided on one surface thereof with an adhesive surface formed by the application of a thermosensitive adhesive agent and attach the heated label uniformly and tightly to the surface of a flexible article. A further object of this invention is to provide a label-attaching die which is capable of effecting the attachment of a label so as to preclude the possibility of the attached label being peeled off the surface.